Is China's newly built quantum crypto-network really unhackable?

It looks like China is the latest to apply quantum cryptology to create a supposedly unhackable network. But just how valid are these claims?

Looking at photons alters them - so attackers will concentrate on end links

The Chinese quantum crypto computer project in question (http://www.bbc.co.uk/news/world-asia-40565722) in the city of Jinjan, is being promoted by state media as a milestone with 200 military, government and financial sector workers taking part in the trial.

The development of quantum crypto networks is not new; research has been going on for decades and such networks already operate in the West. However, over here they tend to research projects whereas the Chinese development is being carried out with commercial partners.

Joe Pindar, director of data protection product strategy at Gemalto, told SC that what China has achieved is "significant, and is the closest we have got to reasonably using the phrase unhackable".

What makes the Chinese system different to other developments is distance. "Where the technique was previously limited to city-based links" Pindar continues "it is now open to satellite networks."

But is it really correct, or indeed wise, to call any network unhackable?

Andrew Lord, head of optical research at BT, speaking to SC Media said "No, but it does offer unprecedented levels of security." So what actually happens is the quantum key distribution mechanism itself is secured by the principles of quantum physics. These state that it is impossible for a hacker to observe the single photons carrying the keys, without changing them.

Lord points to three further things to bear in mind when implementing this idea in practice however:

1. "QKD is protecting against tapping into the optical fibre during transmission, but the ends of the links, from where the fibres terminate, through the switches and connections to computers etc will not be protected by QKD unless it is actually running from the end point itself."

2. "The actual implementation has to be sound. For example the system has to be robust against attackers trying back-door or man-in-the-middle attacks, such as shining their own powerful light into the system to try to read what is happening inside the QKD receiver. Sound implementation is perfectly possible, but is additional to the basic quantum physics."

3. "Once the keys are distributed, they are used to encrypt data using a conventional private-key algorithm such as AES256. Although this is thought to be very strong indeed, it is still potentially vulnerable to fast computers. However, a brute-force search through all the possible keys would take a vast amount of time and there are no known algorithms, even running on quantum computers, that could significantly speed this up."

All of these aside, there's then the question of whether we even need quantum crypto? We turned to encryption whizz Richard Moulds, general manager at Whitewood Security, for his thoughts.

"We don't know for sure that we do need quantum crypto" Moulds told SC, continuing "for decades, we've had a strong suspicion that an attacker with a quantum computer can calculate secret keys and break many, but not all, of our existing crypto algorithms. But in the absence of actually having a strong quantum computer to test with, we can't be certain."

Uncertainty is the enemy of security. Yet it takes at least a decade to develop and commercialise a new crypto algorithm, maybe even longer for one that is quantum-safe. "The point is that if we wait until we know for sure that we need one" Moulds explains "it will be too late to develop one."

So there's effectively a race going on at the moment between the mathematicians and the physicists to address the quantum threat. "The mathematicians believe they can solve the problem by simply switching to a newer set of algorithms" Moulds concludes "whereas the physicists believe we need to fight fire with fire and switch to an entirely new method of communications for keys that itself relies on quantum mechanics." If the mathematicians are right then all the world needs is a software upgrade; if not then we face a very expensive transition to new hardware and a crash course in quantum mechanics.

We'll leave the last word to Paul Ducklin, senior technologist at Sophos. "It's a massive step from having an unhackable technique to building an unhackable implementation of it" he told SC Media "and it's an even bigger step from having an unhackable QKD implementation to having an unhackable network."

As a cynic might say: for the dictionary definition of 'unhackable' see 'hubris'...

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